Structure of raster in melolonthine larvae

Ultrastructural and electrophysiological investigations carried out on larval rasters of Rhopaea magnicornis Blackburn, Lepidiota frenchi Black, and Antitrog consanguineus Blackburn revealed that the raster is a complex of mechanoreceptive setae. Chemical and morphological investigations provide no evidence that the raster is a site for chemical emissions: however, species differences in hydrocarbon profiles were found among larval cuticle samples. Ultrastructure of the setae (pali) show that each seta is innervated by a single dendrite which ends in a tubular body at the base of the seta. The connection with the seta is on the proximal side, which corresponds to the production of a phasic-tonic electrophysiological signal on downward deflection. The dendrite is surrounded by a granular, electron-dense sheath which has inwardly directed arms distally and outwardly directed arms proximally. Two sheath cells are present, 1 forming a large receptor lymph cavity which is lamellate and lined with electron-dense material